9 rubber stamps cost $9.09. Which equation would help determine the cost of 8 rubber stamps?
Answer: There are several equations that could help determine the cost, each with a slightly different approach. Let $x$ represent the unknown cost of 8 rubber stamps. Since 8 rubber stamps cost $x$ , we have the following proportion: $\dfrac{8}{x}$ We can write the fact that 9 rubber stamps cost $9.09 as a proportion: $\dfrac{9}{\$9.09}$ The cost changes along with the number of rubber stamps purchased, and so the two proportions are equivalent. $\dfrac{8}{x} = \dfrac{9}{\$9.09}$